The term "pressure sensitive adhesive" as used throughout the instant specification refers to adhesives that can be adhered to a surface and yet can be stripped from the surface without transferring more than trace quantities of adhesive to the surface, and can be re-adhered to the same or another surface because the adhesive retains some or all of its tack and adhesive strength.
Pressure sensitive adhesives of the prior art are generally of two generic types. The first type, organic pressure sensitive adhesives, are known in the art to have the requisite physical properties and low cost to make them suitable for a variety of applications. However, the organic pressure sensitive adhesives have been found to be unsuitable for applications requiring adhesion to low energy surfaces, improved weatherability, high low temperature flexibility and good high temperature stability. Thus, organic pressure sensitive adhesives have generally been found to be unsuitable for use in outdoor applications such as outside graphics, automobile striping and for use in bonding plastics where temperature extremes are encountered.
The second type, silicone pressure sensitive adhesives, are also known in the art and are employed in a wide variety of applications, such as pressure sensitive adhesive tapes. The silicone pressure sensitive adhesives exhibit improved weatherability properties over the organic adhesives, such as exhibiting excellent adhesion to very low energy surfaces, flexibility at low temperatures and are chemically stable at high temperatures.
Special mention is made of Traver, U.S. Pat. No. 5,096,981 which discloses that less than 100 parts per million of certain metal salts can be added to a pressure sensitive adhesive comprising a homogeneous mixture of two intermediate pressure sensitive adhesives.
The excellent properties of silicone pressure sensitive adhesives have created an increasing demand for still better adhesives which will withstand the higher operating temperatures of modern equipment and processes. Thus, it would satisfy a long felt need in the art if a silicone pressure sensitive adhesive could be developed which exhibited still further improved high temperature stability over the silicone pressure adhesives of the prior art.
To this end, the present invention provides a novel silicone pressure sensitive adhesive which exhibits improved high temperature stability, passing aging tests at temperatures above 550.degree. F. Such novel silicone pressure sensitive adhesives and their improved high temperature properties are exemplified in the working examples of the present invention.